1. Field of the Invention
The present invention relates to a navigation system which conducts route searching and route guidance to a predetermined destination.
2. Description of the Related Art
Various vehicle navigation systems which conduct route guidance to a destination from a point of departure or current position through passing points, with display and voice guidance, have been proposed. The typical vehicle navigation system stores guidance data in its information storage unit, inclusive of map data, data for features of crossings and passing points and display and voice data, searches the map data to determine an optimum route from the current or departure location to the destination (route search), and provides route guidance. Thus, the typical vehicle navigation system includes an input/output device for inputting and outputting information related to route guidance, a current position detection unit for detecting information relating to the current position of the vehicle, an information storage unit for storing navigation data necessary for determination of a route and display/voice guidance data or the like necessary for route guidance, and a central processing unit for conducting route search processing, display guidance processing necessary for route guidance, and control for the overall system.
Generally, the information storage unit, as shown in FIG. 13, includes indexed files of map data, search data, guidance data, map matching data, destination data and the like, i.e. provides a database storing all data necessary for the navigation system. As an actual storage medium, a CD-ROM is often used for this purpose. The stored navigation programs will include both OS (operating system) and application programs. The application programs include a map drawing program, route search programs, route guidance programs, current position calculation programs, and destination setting operation control programs. The map drawing program, the route search program, the route guidance program, the current position calculation program, and the destination setting operation control program are executed utilizing map data, search data, guidance data, map matching data and destination data, respectively. Because the current position calculation program can calculate a current position using map data, by using the same map data for the map drawing program and for the current position calculation program, omitting duplication of map data, it is possible to reduce the total amount of data.
The present position calculation section detects current location position by comparing direction information and distance information obtained from signals of the relative direction sensor, the absolute direction sensor and the distance sensor with map data or map matching data. Responsive to input of the destination or to an instruction to execute a route search, the route search program is executed to search for an optimum route using map data. When guidance is started, the route guidance section displays a map indicating direction of travel relative to the current location, outputs remaining distance to an intersection, identifies a feature or point being passed, travel direction at an intersection, information pertaining to the identified feature or point, utilizing guidance data associated with the determined route, by visual display and voice.
The conventional vehicle navigation systems are generally classified as one of two types. In one type, as shown in FIG. 14(b), only data is stored in a CD-ROM, while application and OS programs are stored in a ROM of the central processing unit. In a second type, shown in FIG. 14(a), a program and data are stored in a CD-ROM and a program memory area consisting of a RAM or a flash memory is provided in the central processing unit to read a program each time it is required.
The navigation map storage media may include a map for the entire country (nation-wide map) stored in a single storage medium, local map storage media for each local area, with the entire country covered by a plurality of such local map storage media and sightseeing map storage media in which additional information such as tour guidance is added for a particular area. To provide these different map media with compatibility so they can be processed in the same apparatus, data format is usually standardized. However, any of the following circumstances may be encountered:
(1) The format for stored data is different as between the different storage media;
(2) Although the format of the stored data is the same, map information such as position coordinates, name and shape is different; or
(3) The format of the stored data, and data type and contents such as position coordinates, name and shape are all in conformance with a uniform standard.
However, because as mentioned above, the data media include a nation-wide version, local versions and genre-based versions (for sightseeing, leisure, and the like), and because some local versions represent different geographic divisions, and a given program is provided with a plurality of data CD-ROMs, if the CD-ROM is changed, destination and search conditions (express road priority or the like) must be reset and an instruction for execution of route search must be input, which operations required of the user have proven inconvenient. Even in the case of identically formatted local versions, if they are developed separately, even if they use the same coordinates, information as to road numbers, intersection and exit numbers and search conditions may be different. Additionally, because a guidance route is usually memorized in the form of road numbers and intersection/interchange/exit numbers, if the CD-ROM is replaced after the guidance route has been determined by route search and memorized, the route search function becomes disabled.
Further, with regard to the above-classified three different sets of circumstances, in case (1), a new disk replacing the former disk cannot be activated. In case (2), although the disk can be activated because its data format is the same, because the data content is different it is impossible to provide guidance for a route determined before the new disk was read. In case (3), although it seems that route guidance before the disk is replaced is possible because the data style and content are based on the same standard, because the data content is different, it is impossible to provide complete compatibility. For example, a road which exists in a local version may not exit in a nation-wide version. Thus, to receive appropriate route guidance, each time a disk is replaced, it is necessary to again set a destination, to again set a search condition and to repeat the process of route determination from the beginning, at an inconvenience to the user.
In conventional navigation systems, by changing the CD-ROM between various CD-ROMs for different geographic areas, purpose or genre, such as for sightseeing, golf, and the like, it is possible to achieve smoother and more comfortable guidance. Thus, a plurality of the CD-ROMs are typically stored in a single case so that the CD-ROM from which information is to be read, at the command of a user, can be changed manually.
However, in a conventional navigation system in manually changing the CD-ROMs from which information is to be read, among a plurality of stored CD-ROMs, no attention is paid to the information content of the CD-ROMs. For example, in using a navigation system in which five CD-ROMs are stored, a CD-ROM in the first position of the changer is moved to an optical head and by the next command for change, the second CD-ROM is moved to the optical head. In this manner, only a mechanical change is performed.
In other words, the conventional navigation system does not automatically take into account the information stored in the CD-ROMs when changing CD-ROMs. Thus, by a manual change command through a switch input, a new CD-ROM is set on the optical head and information of this CD-ROM is read and its contents are displayed on the display screen. Then, the user can judge whether or not the new CD-ROM is that desired. Therefore, if the replaced CD-ROM is not that desired, the user must again input a CD-ROM change command to the navigation system, a very troublesome procedure.
Thus, in the prior art system, in changing CD-ROMs, the new CD-ROM to be selected cannot be identified with certainty and the desired CD-ROM cannot be selected rapidly. Because a sightseeing CD-ROM, a leisure CD-ROM, a golf CD-ROM and/or a detailed road map information storage CD-ROM for the same area are all present in the changer, even if the road map information recorded on the CD-ROMs is the same, the user may become confused as to which CD-ROM should be selected and must confirm the contents of all the CD-ROMs.
In addition, the changing of CD-ROMs is accompanied by two large time lags, the time required to mechanically move the new CD-ROM to the optical head and the time required to read information from the CD-ROM and to display it on the display screen. Thus, in a navigation system employing a plurality of CD-ROMs which may be loaded, selecting a CD-ROM appropriate for the current location and type of destination is very difficult for the user.
In a navigation system in which only a single CD-ROM can be loaded, the user has to replace the CD-ROM manually. Thus, if the vehicle moves from the geographical range of one local version CD-ROM across to the geographical range of another local version CD-ROM, the user must replace the CD-ROM while the vehicle is moving. Such replacement of the CD-ROM is not easy during movement of the vehicle. In addition, when the CD-ROM is replaced, a route re-search must be conducted based on road information contained in the new (replacement) CD-ROM. Thus, the navigation guidance is stopped for a specific time just after the replacement.